5.1.6.8 Manufactured assemblies employing hose or flexible connectors, where the station outlet/ inlet attached to the piping is not fully and immediately accessible (i.e., cannot be manipulated without the removal of panels, doors, and so forth), shall have station outlets/ inlets with the following additional characteristics:

(1) They shall be gas-specific connections with positive locking mechanisms that ensure the connector is firmly seated and cannot detach without intentional actuation of the release (e.g., D.I.S.S. connectors).

5.1.3.5.2 Permitted Locations for Medical Gases. Central supply systems for oxygen, medical air, nitrous oxide, carbon dioxide, and all other patient medical gases shall be piped only to medical gas outlets complying with 5.1.5, into areas where the gases will be used under the direction of licensed medical professionals for purposes congruent with the following:

NFPA states that all outlets/inlets need to be tested annually. How would you test those outlets?

I do not know of anywhere within NFPA 99 that states outlets / inlets need to be tested annually. There is a section in the annex (A5.1.15 I believe) that mentions annual testing. I believe the wording used in 5.1.14 is "periodic".

Cary, you are correct - the "annual for outlets" is a facility specific item, not mandated anywhere.

Nor does anyone, anywhere, talk to intentional abandonment of a system.

So I agree with Don that removal is the "Right" answer. There are so many problems that hidden outlets raise which can't really be answered (leakage, decay with time, backflow/contamination if the valve is closed and the pressure leaks away, opening by the curious/malicious, misuse)